Bosch Dishwasher SMU68M05AU - E24 error [FIXED]

[Lorenzo_1]

Thought a short post on this repair might be helpful, as Error Code E24 (Check Water) seems to be commonplace but none of the suggested fixes I could find online was helpful in this case.  Symptom was failure to drain water fully during the wash cycle, resulting in a program halt. Common suggested fixes are checking for blockages in drain hoses/outlets and inlet hose, cleaning the filter system, checking for debris blocking the drain pump impeller etc.  In this case I tested and cleaned all these systems but the fault persisted.  There is a manual for similar Bosch models available online - but it takes some diligent searching to find (thought it best not to post link here). That was helpful in describing how the quite complex system works and giving some resistance tests for pump motors and solenoids, but gives no guidance on error codes. Seems the microprocessor logs error signals but they're only accessible with proprietary Bosch hardware and software.

Resorted to oscilloscope tests to see whether control board was driving the pumps OK.  Signals there all looked OK (pulsed square waves), but it became apparent that the program stop was not correlated with the start or end of pump drive signals.  Instead, it happened only when the water conservation system was trying to store water in the reservoir attached to the LHS of the machine.  That pointed to the flow sensor on the reservoir - this has an impeller adjacent to the flow channel with magnet that opens/closes a microswitch (photo attached). CRO quickly showed the switching impulses from it were intermittent, suggesting the switch was failing. $45 later problem solved. High price for such a small board, but cheaper than a new dishwasher or a service call. Searched for a replacement microswitch but more trouble than it was worth.

Another task to do while you have the system open is to clean the flow channels and float (drainage hose ventilation valve) shown in the reservoir photo.  They get gunked up badly and float doesn’t operate.  I removed the tank, flushed it with water and then hot concentrated dishwasher detergent, leaving it to soak.  Note that you have to remove two plastic screw fittings (inlet & outlet) from inside the dishwasher before the tank will come free. To shift the last of the caked on goo I had to resort to careful use of an air chisel to vibrate it free!  That worked fine – though it took quite some time.

[ebastler]

Thanks Lorenzo; nice summary of your repair!

For future reference: There is a great collection of repair briefs for dishwashers, washing machines etc. from Bosch/Siemens/Neff here:
https://forum.teamhack.de/filebase/file-list/

Specifically, disassembly and most common repairs of their dishwashers:
https://forum.teamhack.de/filebase/download/19/

(In German, I'm afraid, but worth the effort. BTW, while there is some hacking involved in some of the repairs, the site owes its name to Mr. Hack's last name. )

[Lorenzo_1]

Thanks for the links - there's some really useful stuff in there. Didn't search on non-English sites. My German's non-existent but Google translate helps a bit and the photos are often self-explanatory.  My antivirus detected a malicious page in one of the pdf files on the first link - not sure if it was real or not. Most were OK. I'm sure some of my other European appliances will decide to play up as soon as I turn my back. 

[ornea]

Thanks for your post Lorenzo_1.  I though I would add my experience and ask some questions. 

My machines (SMS63M08AA which looks similar) behavior at start of cycle, it will run the siphon pump, then run the recirc pump and switch back and fourth eventually throwing an E24.  If I open and close the door at the right point the cycle will begin but again fail later in the cycle (sometimes)

I have spent many many hours with E24 finding many red herrings that I was convinced was the issue, some of these follow.

1. PCB edge connectors seem problematic.  Measuring winding resistance of drain pump for example would have the reading bounce around if the wires were ever slightly moved.  So I cut some of them off and soldered direct. No fix

2. Flood water detector micro switch also had the Resistance values bounce around each time it was operated.  Solution, dismantle and clean micro switch. Now both NC and NO contacts shows ~0.2 ohms  when operated. In this case I don't think it was the contacts that were high resistance but where the toggling pole connects to the frame its in. Confident this was the cause but no fix.

3. Flow channel reed switch. I observed if I  operate the reed switch by introducing a magnet at the right part of the startup cycle it begin filling and the cycle would start.  If I do this when the system has not requested a fill (ie the solenoid is off) or do it too much it generates E16, understandable.  My reed switch appears to be operating ok. I did suspect it but tests ok.  I also noticed that when the system is at rest the reed is Normally Closed, I arranged a magnet to change this to Normally Open and the first test cycle began without a hitch. i thought i was onto something but next cycle it failed.

My Questions:-

1. I wanted to observe the drive signals to the pumps with a scope but not sure how to connect the ground lead.  I also want to look at the supply rails but again concerned about where I should connect the ground clip.  How did you do this?

2. In the flow path you mention a "drainage hose ventilation valve", is that a simple mechanical structure or is there a sensor in there.  Mine is gunked up. Today I am going to clean but curious if there is a sensor there to detect a blockage.  I dont thinks so. I cant see wires or any sensor there but is gunked so hard to see.

3. How do you enter a Test Cycle or Test Program so I dont have to wait 2 hours to know if it ran ok.

I will continue to update this thread particularly if I find the cause.

[ornea]

Lacking intelligent moves I decided to replace the inflow reed switch that tested 100% using multimeter and magnet with another that tested ok but with contact resistance around 1.5ohms.

To my surprise the first rinse cycle started and completed without a hitch  but the first normal cycle error'ed E24  .  However the next attempt at a normal cycle proceeded ok.

So 2/3 aint bad. but not right.

I have been pondering:-
1. how does this machine know when the side tank reservoir is full (does it count pulses on the inflow sensor, i would think not accurate enough for that)  and
2. how does it know when the sump is full enough.  At the start of a cycle it dumps the side tank into the sump, starts recirc and then adds more water.  How does it know when to stop.  I see no sensors. Perhaps it measure back EMF from the recirc pump.  There is a turbidity sensor but that is submerged after about a cup of water has entered the system.

[xavier60]

I fixed my brother's dishwasher a long time ago. It could have been the same model and I can't remember the error code, it was pump related. I found a faulty dual opamp in a pump related area of the board.

[franner]

Exactly like fault with my SMS50E22AU/07. have a look at this link I found
https://appliancefault.com.au/faults/dishwasher-faults/bosch-dishwasher-error-codes/
E24 fault at the start - solution suggested by Bosch code list is non-intuitive. Dishwasher does a couple of stage checks to see if water exists by running both wash pump and then the drain pump and measures the current, and if it doesnt like it then it thinks there is excess water, and so tries the wash pump again and then it stops dead and throws up E24. Yet if you open and close the door at the start of stage 3, then it works fine. Mine faulted after 2 years and as been like this for another 8 years, nothing else has failed since. Still works fine when you open/close the door early at the third stage (if you hear water filling after 2nd stage then its away). Looks like the new version heat pump, part number Heat pump 00654575  replaces the original pump, has a different part number so I would say Bosch know its dodgy, and dont want to admit it. Bosch Shareholders obviously dont want to recall thousands of these. New pump is $281 to me, not sure whether I want to waste that much. Would say a lot of them have gone to the dump, and Bosch do not feel responsible one little bit. Might just be the stiff impellor as suggested, or might be the bearings, but bearings feel OK to me, special looking thing in bits. Need a hack for the impellor?

[franner]

Hack option 2:
Figure out the current measuring system, hack into it with an interface that reduces the current signal for the first 2 minutes by some adjustable % range, to allow for the stiff impellor issue?
Adjustable, and find optimum value by test in order to retain best compromise for intended protection function?

[ornea]

I put resistors in series with the motor and had many successful runs but it eventually error'ed.

The latest post have renewed my enthusiasm to experiment again.

Maybe a door open sim hack that operates shortly after the cycle starts.

[Lorenzo_1]

Hi Ornea.  Firstly apologies for this late response - have had a busy time lately and haven't kept up with postings.  Re your earlier questions:

Manual indicates that the flow into the machine is calculated by pulse counting from the reed switch on the flow sensor.  Seems sensible that reverse flow into the reservoir would be measured the same way.

No sensor in drainage ventilation valve - just a float valve.  You've doubtless sorted that out already.

I haven't found any self-test diagnostics accessible through start-up key presses or the like. 

The drain pump is easy to remove for testing. It has a single locking tab at the top and when this is released just twists anticlockwise and pulls out.  Resistance should be 80.5 ohm.

With the drain pump removed and water turned off(!) you can do a quick start-up test of the drain pump uninstalled.  IIRC when machine starts it send forward, reverse and forward pulses to the pump in a few bursts and then, presumably if it confirms there's nothing jamming the pump, runs it at speed. Gives you a chance to see if the drain pump is getting a reliable feed and/or is mechanically faulty.

I had another E24 error come up just recently, which wasn't related to the flow sensor.  It was intermittent for a while, then came on every time we used the machine but didn't prevent cycle completing, and finally stopped it completely.  In this case, turns out it was caused by water under the float sensor in the base of the machine (it's a 4-5" round polystyrene float adjacent to the motor housing on LHS with a simple microswitch above it).  Removed and cleaned, tested switch (OK), checked for leaks by adding some food colouring to clean water in the reservoir and monitoring for a few hours (no sign of any), reinstalled everything and it's been working fine since.  I suspect the overflow/leak was a very slow one over a longish time that had gradually built up enough water to activate water level switch at first intermittently and eventually permanently.  Some posters suggest simply tilting the machine to fix E24 errors caused by this - but it's easy to access from the front of the machine and you can confirm whether this is the cause or not. Key is to remove lower half of the door panel by removing 6 screws from  inside cover and pulling it off.  Then the kick plate etc can be removed for access.

It's clear there are multiple causes for this E24 error code.  Oddly enough, the service manual doesn't list any error codes or their possible causes.  Presumably expects you'll have access to their diagnostic system.

[mace]

Hello and thanks for all giving this feedback, I was able to fix my now above 10y old Bosch SMU49 with information here, added with some new that I want to share with forum.

First I got E24 every now and then for last 2 years. Then in last August it was persistent. So I replaced drain sensor and pump, as sometimes there was water visible in drain well. Actually it turned out that pump has some filth around the axis and that made the rotation quite difficult. So based on resistance, it seems the pump is ok. Dishwasher worked for 6 months, but then suddenly E24 was persistent again. This time I decided the only possible cheap spare that could be broken is the flow through sensor. So I replaced that. After reset dishwasher worked three times and then again E24 was persistent. So I decided to measure all cables and connectors on control board end. All motors and sensors seemed to be good in terms of resistance. I reconnected all wiring and ops, I got E20 !!!

I started to look the connectors and actually those seem to be quite "cheap" in terms of quality. I used a pin to reform all connecting surfaces in all connectors going to pumps and sensors, on both periphery and control board side. And voila, now everything is working. Even the eco program, that has refused to start at least for 4-5 years. So my conlusion is that as motors/pumps vibrate, the connectors are getting mechanically stressed and little by little those lose firm contact. This even might hide that when a motor is operating, the motor or sensors get uneven connection and thus the operation fails to give expected signal to the program.

[ornea]

Interesting, I have just re-started attempted repair/cludge fix of mine.

Since the door opening at the right point in the cycle seems to kick it along I thought I would build a circuit that simulates door open 60secs or so after start is pressed.

However, I may again follow the path you have taken.  I too tried reforming those connectors that as you say look cheap and suss. I used a pin as you did and wedged toothpicks etc in there to add more force to ensure a good connection. In the past in worked for about 5 cycles then as always intermittent again.

I started using other techniques to ensure good connection including soldering the pump connections. After your success I may simply solder everything direct to the board and eliminate the connections as a possible source of failure once and for all.

[learjet23]

Did anyone ever successfully build an open door circuit (hack)? If so how did you accomplish it?

Cheers,
Mark

[Kleinstein]

A common problem with the Bosch and likely most other types too is some dirt getting in the pump and causing problems.  One can usually remove the filter in front of the pump and than clean it carefully (there could be sharp objects in the pump). How to clean the pump is usually desribed.

With quite some of Bosch dishwacher the filter really deserves a few  : when removing it to clean the filter the dirt falls in the pump. In addishen the overflow path has no filter at all and dirt can fall in there.